A system structure of System Architecture Evolution (SAE) is illustrated in FIG. 1. The system structure of SAE in FIG. 1 is described as following.
User Equipment 101 (hereinafter referred to as UE) is a terminal device used to receive data. 102 EUTRAN, also called ENB, is a radio access network of the LTE SAE, for providing interface through which an LTE mobile station accesses the radio network. Through interface S1, EUTRAN connects to a mobility management entity (MME) 103 and a user plane entity Serving Gateway (S-GW) 104 in the mobile station. 103 MME is adapted for managing mobile context, session context for the UE, and holding user information on security. 104 Serving Gateway primarily provides a function of user plane. An interface S1-MME is adapted for establishing radio access bearer, forwarding messages from UE to MME through a wireless access network. The combination of 103 MME and 104 Serving Gateway is similar to the original 106 SGSN (general packet radio service (GPRS) supporting node). It is possible that both MME and Serving Gateway locate at the same physical entity. 105 PDN Gateway is adapted for the functions like accounting, legally monitoring, etc. And it is possible that both the Serving Gateway and the PDN Gateway locate at the same physical entity. 106 SGSN provides routing for data transmission in existing UMTS. An existing SGSN finds a corresponding gateway GPRS supporting node (GGSN) according to an access point name (APN). 107 HSS is a home subscription sub-system for the UE and is adapted for storing user information such as the current location of UE, address of the serving node, security information on the user, activated packet data protocol (PDP) context for the UE and so on. 108 PCRF provides QoS policy and accounting rules through interface S7.
In general, a user data stream reaches the 104 Serving Gateway through 105 PDN Gateway. Then, through the GPRS tunnel protocol (GTP) channel, data is sent by the Serving Gateway to the ENB where the UE locates in, and now it is sent by the ENB to corresponding UE.
HNB refers to a Node B applied in a home. It also can be applied in such site as a university, a company and so on. HNB is a plug and play device. Difference between an HNB and a general macro node B is that: in general not all UEs can access an HNB. For example, only the UEs in a user's home or that are allowed to access the HNB can access the corresponding HNB. And for the HNB in a company, only the company's staff and its allowed partners can access the HNB. The HNB group (e.g., the HNB in a company) bearing the same access subscriber cluster is called CSG (closed subscriber group). No interface X2 (interface between Node Bs in SAE) exists between general HNBs (e.g., the HNBs in homes) or between an HNB and a macro Node B. Through interface S1, a UE switches between HNBs or between an HNB and a macro Node B.
For an HNB applied in a company or university or the like, a UE frequently moves between two HNBs in the same company. In this case, the switch is always implemented through interface S1 so that great delay causes and efficiency is very poor. In addition, information such as radio resource management and so on can not be exchanged between two HNBs in the same company so that resources can not be utilized effectively.